1. Field of the Invention
The present invention relates to a color television receiver having an automatic adjustment system, and to a process for accomplishing the automatic adjustment.
2. Description of the Prior Art
In known color television receivers, the pulse stages for the screen correction, the horizontal deflection and the vertical deflection are controlled on an analog basis. These control stages are partially integrated and partially equipped with discrete modules.
In order to control the horizontal deflection output stage, an oscillator generates horizontal frequency oscillations. These are compared with the line sync pulse on the transmission side and the line return pulse on the receiver side in phase monitoring circuits (for example, phase-locked loop). The regulating voltages generated upon phase differences serve for the synchronization of the oscillator (VCO). In general, phase relation and base frequency of the oscillator are provided as adjustment positions.
In order to control the vertical deflection output stage, a sawtooth generator (for example, blocking oscillator circuit) is directly synchronized by means of the vertical sync pulse and drives the vertical deflection output stage by way of a driver circuit. The current reduction caused by the heating of the deflection coil is compensated by way of a countercoupling. Here, generally, frequency, picture height and linearity are the adjustment magnitudes.
On the picture screen, the deflection midpoint of the electron beams does not coincide with the curvature midpoint of the screen. Therefore, a square picture on the screen is concavely distorted with its vertical lines in the shape of a pillow. The distortion of the horizontal lines in modern inline color picture tubes is generally already compensated by means of the deflection field. For correction of the so-called east/west pillow distortion, for example, a known diode modulator circuit is employed which modulates the voltage via the horizontal deflection coil in such a manner that the line deflection current is greater in the center of the picture than at the beginning of the picture and at the end of the picture and, viewed by way of image frequency, has a barrel-shaped course. Adjustment magnitudes of the diode modulator circuit are the modulation degree via image frequency, symmetry (so-called trapezoidal correction) and picture width.
In the analog signal stages for the video circuit and the PAL coder, for example, the magnitudes for the white value, the gray balance and the beam current limitation are adjusted.
In the positions for the magnitudes to be adjusted, which are mentioned above for the individual pulse or, respectively, signal stages, potentiometers are inserted which are adjusted by hand during or after the device assembly according to a visual evaluation of a test picture or according to the measurement of an electronic magnitude. These adjustments are therefore usually subjective and, moreover, cost intensive.